Water is transported through biological membranes by two pathways: lipid diffusion and water channel-mediated transport. Water channels, also named aquaporins, are present in many cell types and tissues, plants and lower organisms. AQP2 is one of this family. AQP2 is an important water channel present in principal cells of the mammalian kidney collecting duct to regulate water homeostasis. In addition to the on-going exciting research on AQP2 trafficking, there are emerging data from animals indicating that besides their classic role in water or small solute transport, aquaporins may exert additional roles in critical biological processes such as: neural signal transduction, cell migration and angiogenesis. Studies in a mouse knock-in model of AQP2 T126M, a mutation causing ER retention of AQP2, showed a urinary concentrating defect (nephrogenic diabetes insipidus, NDI), and unexpectedly, neonatal mortality from renal failure. Biopsy of homozygous mice revealed kidney tubular necrosis and cyst formation. This unusual finding prompts us to investigate a potential novel function of AQP2 in kidney development. Our preliminary study suggests that AQP2 indeed plays a role in epithelial cells migration and adhesion. Therefore, we propose that AQP2 plays a critical role in the development, maturation or maintenance of renal tubular integrity via its effects on epithelial migration, cell-cell and cell- matrix interaction. For these studies we will take advantage of the well-characterized zebrafish system to investigate these novel functions of AQP2 in vivo. Specifically, we will investigate spatial and temporal expression of an AQP2 orthologue in wild-type zebrafish and zebrafish with kidney cysts, and investigate any alteration of AQP2 trafficking under these conditions;2) investigate roles of AQP2 in development/maturation of the pronephros in zebrafish by knocking down AQP2 function using morpholinos, and via tissue specific overexpressing of AQP2 with mutations that produce trafficking defects and migration defects in vitro. Our proposed studies will contribute not only to the understanding of the molecular mechanism underlying a novel function of AQP2, but also provide understanding of the unexpected contribution of a classic channel protein to other important aspects of epithelial cell biology. PUBLIC HEALTH RELEVANCE: Water channels, also named aquaporins, are present in many cell types and tissues, plants and lower organisms. They transport bulk water rapidly and provide a major pathway for transmembrane water transport. AQP2 is one of this family, and is an important water channel present in principal cells of the mammalian kidney to regulate water homeostasis.